Recombinant Human Probable palmitoyltransferase ZDHHC20 (ZDHHC20)

What is the basic function of ZDHHC20?

ZDHHC20 functions as a palmitoyl acyltransferase that catalyzes the S-acylation of proteins in a two-stage process: auto-S-acylation of the conserved cysteine in the DHHC motif by acyl-CoA (commonly palmitoyl-CoA), followed by S-acyl transfer to substrate protein cysteines. This post-translational modification plays integral roles in protein localization, stability, and function. ZDHHC20 is one of 23 known human ZDHHCs that collectively acylate over 3,000 cysteine residues across approximately 12% of the human proteome .

The enzymatic activity of ZDHHC20 is dependent on critical residues within its catalytic domain. Studies have shown that two residues, Cys156 and Phe171, in the acyl-binding cavity of ZDHHC20 are essential for its catalytic activity . This palmitoylation activity modifies downstream substrates, affecting their stability, localization, and function within the cell.

What is the structure and cellular localization of ZDHHC20?

ZDHHC20 contains a four-pass transmembrane (4TM) helix domain with a conical transmembrane lipid-binding pocket adjacent to the cytosolic catalytic site . The three-dimensional structure of ZDHHC20, as analyzed in previous research, confirms its two active sites involved in the palmitoylation modification process . This structural arrangement is critical for ZDHHC20's function as it creates a specific environment for substrate recognition and palmitoylation.

Regarding cellular localization, immunofluorescence confocal microscopy has shown that ZDHHC20 is predominantly localized in the cytoplasm, where it can interact with its substrates. For example, it has been observed to colocalize with YTHDF3 in the cytoplasm of pancreatic cancer cells .

How do researchers detect ZDHHC20-mediated protein palmitoylation?

Several methodological approaches are used to detect and analyze ZDHHC20-mediated palmitoylation:

• Acyl-biotin exchange (ABE) assay: This technique allows for the detection of S-acylated proteins by replacing palmitoyl groups with biotin, enabling subsequent purification and identification of palmitoylated proteins .

• Palmitoylation liquid chromatography-mass spectrometry analysis: This approach enables the identification of specific palmitoylated proteins and their modification sites. For example, this method identified 97 proteins with 123 cysteine sites that are palmitoylated in a ZDHHC20-dependent manner in hepatocellular carcinoma .

• Chemical-genetic systems: Structure-guided engineering of paired ZDHHC "hole" mutants and "bumped" chemically tagged fatty acid probes enables selective labeling and identification of specific ZDHHC substrates. This approach has been applied to ZDHHC20 to identify its substrate networks .

What experimental models are commonly used to study ZDHHC20 function?

Researchers employ various experimental models to investigate ZDHHC20 function:

• Cell line models: Human cancer cell lines such as PANC-1, BxPC-3, and CAPAN-1 (pancreatic cancer), and HEK-293 and Vero E6 (kidney-derived) are frequently used to study ZDHHC20 function through overexpression, knockdown, or knockout approaches .

• Genetically engineered mouse models: ZDHHC20 knockout mice have been used to investigate the role of ZDHHC20 in cancer development. For example, in hepatocellular carcinoma (HCC), chemical carcinogen diethylnitrosamine (DEN)-induced and DEN combined CCl4 HCC models were used in ZDHHC20 knockout mice to investigate its role in HCC tumorigenesis .

• Inducible expression systems: Tetracycline-inducible Halo-tagged ZDHHC20 has been developed to investigate the impact of targeted ZDHHC20 degradation on substrate palmitoylation .

What is known about ZDHHC20 substrate specificity and its major substrates?

ZDHHC20 exhibits substrate specificity despite the lack of a consensus sequence in protein substrates beyond the requirement for a free cysteine. Key identified substrates include:

• YTHDF3: A m6A reader that interacts with ZDHHC20 in pancreatic cancer cells. Co-immunoprecipitation assays have confirmed the interaction between ZDHHC20 and YTHDF3, but not with related proteins YTHDF1 or YTHDF2, demonstrating substrate specificity .

• Fatty Acid Synthase (FASN): ZDHHC20 palmitoylates FASN at cysteines 1471 and 1881, which protects FASN from degradation via the ubiquitin-proteasome pathway. This palmitoylation competes against ubiquitination mediated by the E3 ubiquitin ligase complex SNX8-TRIM28 .

• IFITM3: ZDHHC20 has been shown to palmitoylate Interferon-induced transmembrane protein 3 (IFITM3). In HEK-derived FT-293 cells, Halo-ZDHHC20 degradation significantly diminished IFITM3 palmitoylation .

• Other reported substrates: ZDHHC20 has also been reported to palmitoylate EGFR in breast and lung cancers, melanoma cell adhesion molecule (MCAM) in melanoma, and other proteins including NCAM1 and VAMP7 .

Chemical-genetic systems combined with proteomics have identified over 300 ZDHHC-specific substrates and S-acylation sites across various human cell lines, providing the first extended substrate networks for ZDHHC20 .

How does ZDHHC20 contribute to cancer progression and prognosis?

ZDHHC20 has been implicated in cancer progression through multiple mechanisms:

• Pancreatic cancer: High expression levels of ZDHHC20 correlate with unfavorable prognosis in pancreatic cancer patients. Analysis of The Cancer Genome Atlas (TCGA) data and the Tumor Immune Estimation Resource (TIMER) database indicated that ZDHHC20 is a poor prognostic factor in pancreatic cancer. Immunohistochemical staining in tissue microarrays showed abnormally upregulated ZDHHC20 in tumor tissues compared to normal adjacent tissues (NATs) .

• Tumor-promoting functions: Knockdown of ZDHHC20 in pancreatic cancer cells resulted in reduced cell proliferation, invasion, and migration. In vivo, ZDHHC20 knockdown led to lower tumor weight, smaller pancreatic neoplastic lesion area, and longer survival time in KPC mice .

• Hepatocellular carcinoma (HCC): Knockout of ZDHHC20 significantly reduced hepatocarcinogenesis induced by chemical agents in HCC mouse models. ZDHHC20-mediated palmitoylation of FASN promoted FASN stabilization by blocking its ubiquitin-proteasome-related degradation, thereby contributing to HCC formation .

• Other cancers: ZDHHC20 has been implicated in multiple tumors, including breast cancer, lung cancer, and melanoma, where it palmitoylates various substrates to promote cancer progression .

What methodological approaches have been developed to identify ZDHHC20-specific substrates?

Researchers have developed sophisticated approaches to identify ZDHHC20-specific substrates:

• Chemical-genetic systems: Structure-guided engineering of ZDHHC20 "hole" mutants and "bumped" chemically tagged fatty acid probes enables selective labeling of ZDHHC20-specific substrates. This approach involves mutations distal to the DHHC active site to minimize interference with catalytic activity while creating steric complementation with matching "bumped" lipid probes .

• Palmitoylation proteomics: Liquid chromatography-mass spectrometry analysis following palmitoylation enrichment has identified 97 proteins with 123 cysteine sites palmitoylated in a ZDHHC20-dependent manner in hepatocellular carcinoma .

• Targeted degradation approaches: PROTAC (proteolysis-targeting chimeras) technology has been applied to specifically degrade ZDHHC20 and assess the impact on substrate palmitoylation. In HEK-derived FT-293 cells expressing Halo-tagged ZDHHC20, Halo-PROTAC-mediated degradation significantly diminished palmitoylation of its substrate IFITM3 .

How can researchers distinguish between ZDHHC20-specific palmitoylation and palmitoylation by other ZDHHC family members?

Distinguishing ZDHHC20-specific palmitoylation from that mediated by other ZDHHC family members presents a significant challenge due to potential redundancy and overlapping substrate specificity. Several strategies have been developed:

What are the challenges in developing specific inhibitors for ZDHHC20?

Developing specific inhibitors for ZDHHC20 faces several challenges:

• Active site conservation: The extensive conservation of the ZDHHC-PAT active site across family members makes development of isoform-specific competitive inhibitors highly challenging .

• Functional redundancy: The well-established degeneracy in the ZDHHC-PAT family means that in some settings, the activity of non-targeted ZDHHCs may substitute and preserve substrate palmitoylation, potentially limiting therapeutic efficacy .

• Alternative approaches: Due to these challenges, researchers have explored alternative strategies such as PROTAC-mediated degradation of ZDHHC20. While this approach showed promise in HEK-derived FT-293 cells, its efficacy varied across cell types, highlighting the context-dependent nature of ZDHHC20 function .

How can recombinant ZDHHC20 be used in experimental settings?

Recombinant ZDHHC20 can be utilized in various experimental settings:

• Structural studies: Human C-terminally Myc-FLAG-tagged ZDHHC20 has been used for structural analysis to understand the enzyme's mechanism and substrate binding properties .

• Substrate identification: Recombinant ZDHHC20 can be used in in vitro palmitoylation assays to identify and validate potential substrates.

• Interaction studies: Expression plasmids for HA-ZDHHC20 have been used in co-immunoprecipitation assays to detect interactions with potential substrate proteins such as Flag-YTHDF3 .

• Functional studies: Ectopic transfection of ZDHHC20 expression plasmids in cells with relatively low endogenous ZDHHC20 expression (such as BxPC-3 and CAPAN-1 cells) has been used to investigate the functional consequences of ZDHHC20 overexpression .

What are the potential therapeutic implications of targeting ZDHHC20?

Given ZDHHC20's roles in cancer progression, it represents a potential therapeutic target:

• Cancer therapy: Inhibiting ZDHHC20 could potentially suppress cancer progression in multiple tumor types. In pancreatic cancer, ZDHHC20 knockdown reduced tumor growth and extended survival in mouse models . Similarly, in HCC, genetic knockout or pharmacological inhibition of ZDHHC20 mitigated cancer formation in mouse models .

• PROTAC approach: Targeted degradation of ZDHHC20 using PROTAC technology has shown promise in decreasing substrate palmitoylation in specific cellular contexts, suggesting a potential therapeutic strategy .

• Combination therapies: ZDHHC20 may participate in pathways that could be targeted in combination with other therapies. For example, STAT3 inhibition combined with ZDHHC20 knockdown showed effects on tumor growth, suggesting potential for combination approaches .

What are the emerging areas of ZDHHC20 research?

Several emerging areas in ZDHHC20 research hold promise for future discoveries:

• Comprehensive substrate mapping: The development of chemical-genetic systems for ZDHHC20 enables more comprehensive mapping of its substrate network across different tissues and disease states .

• Regulatory mechanisms: Investigation of how ZDHHC20 expression and activity are regulated in normal and disease states. For example, STAT3 has been implicated in regulating ZDHHC20 expression in pancreatic cancer .

• Cross-talk between PTMs: The interplay between ZDHHC20-mediated palmitoylation and other post-translational modifications, such as ubiquitination, represents an important area of investigation. For instance, ZDHHC20-mediated palmitoylation of FASN competes with ubiquitination mediated by the SNX8-TRIM28 complex .

• Disease-specific roles: Further exploration of ZDHHC20's roles in different diseases beyond cancer, including potential implications in infectious diseases, as suggested by its palmitoylation of IFITM3 and potential effects on SARS-CoV-2 spike protein .

What controls should be included when studying ZDHHC20-mediated palmitoylation?

When studying ZDHHC20-mediated palmitoylation, several key controls should be included:

• Catalytically inactive ZDHHC20 mutants: Mutations of critical residues in the acyl-binding cavity (e.g., Cys156 and Phe171) that abolish ZDHHC20's catalytic activity provide important negative controls for palmitoylation studies .

• Palmitoylation inhibitors: 2-bromopalmitate (2-BP), a general inhibitor of protein palmitoylation, can be used to verify that observed effects are indeed due to palmitoylation. For example, 2-BP treatment counteracted the promotive effects of ZDHHC20 overexpression on cell proliferation and invasion in pancreatic cancer cells .

• Substrate cysteine mutants: Mutation of putative palmitoylation sites in substrate proteins (e.g., C1471S/C1881S mutations in FASN) provides critical evidence for site-specific palmitoylation .

• Other ZDHHC family members: Including other ZDHHC family members as comparators helps establish the specificity of ZDHHC20 for particular substrates.

How can researchers overcome technical challenges in ZDHHC20 expression and purification?

Expression and purification of membrane proteins like ZDHHC20 present technical challenges. Researchers can consider the following approaches:

• Expression systems: Mammalian expression systems may better maintain ZDHHC20's native conformation and post-translational modifications compared to bacterial systems.

• Tags and fusion proteins: The use of tags such as Myc-FLAG or Halo can facilitate purification and detection of ZDHHC20. Human C-terminally Myc-FLAG-tagged ZDHHC20 (C-FLAG-D20) has been successfully used in structural and functional studies .

• Detergent selection: Careful selection of detergents for membrane protein solubilization is critical for maintaining ZDHHC20 structure and activity.

• Inducible expression systems: Tetracycline-inducible systems for ZDHHC20 expression can help mitigate potential toxicity issues associated with constitutive overexpression .

What experimental designs best evaluate ZDHHC20 function in disease models?

To effectively evaluate ZDHHC20 function in disease models, researchers should consider:

• Genetic manipulation approaches: Both loss-of-function (knockout/knockdown) and gain-of-function (overexpression) approaches provide complementary insights into ZDHHC20 function. For example, ZDHHC20 knockout significantly reduced hepatocarcinogenesis in HCC mouse models , while ZDHHC20 overexpression promoted pancreatic cancer cell proliferation, invasion, and migration .

• In vivo models: Animal models with genetic manipulation of ZDHHC20 provide crucial insights into its role in disease progression. For example, ZDHHC20 knockdown in KPC mice resulted in smaller pancreatic neoplastic lesions and longer survival .

• Patient-derived samples: Analysis of ZDHHC20 expression in patient samples and correlation with clinical outcomes provides translational relevance. High ZDHHC20 expression correlated with unfavorable prognosis in pancreatic cancer patients .

• Substrate validation: Comprehensive identification and validation of ZDHHC20 substrates in disease models helps elucidate mechanisms of disease progression. For example, ZDHHC20-mediated palmitoylation of FASN promoted HCC formation .